As a photopolymerizable monomer for a negative working photoresist, acrylate resins such as a polyfunctional epoxy acrylate and a polyfunctional acrylate, and epoxy resins are known.
As a resin composition for a positive working photoresist, a combination of a novolac resin and quinonediazide compound is known and has been widely used.
As a negative working photoresist resin composition containing a photopolymerizable monomer having a vinyloxyalkyl group, compositions described in JP-A-60-7165, JP-A-63-71840, and JP-A-64-88538 (the term "JP-A" as used herein means a "unexamined published Japanese patent application") are known. The photopolymerizable monomers having a vinyloxyalkyl group shown in these publications are all vinyloxyalylated products of a novolac obtained by condensing a monohydric phenol such as phenol and cresol, and an aldehyde, e.g., formalin, and are different from the photopolymerizable monomer used in the present invention described hereinafter.
The conventional negative working photoresist using an acrylate resin as a photopolymerizable monomer encounters a problem in that the occurrence of polymerization hindrance with oxygen on hardening of the photoresist is inevitable, and therefore the hardenability of the surface of the hardening film is insufficient. Thus, the photoresist is required to be handled carefully on hardening, such that nitrogen purging is applied, the surface of the photoresist film is overcoated with an oxygen. intercepting layer and the like.
In the case of a negative working photoresist resin composition utilizing the photo ring-opening polymerization of an epoxy group which does not cause a polymerization hindrance with oxygen, the composition has another problem in that the hardening rate is slower than that of the acrylate resin composition.
Thus, the foregoing photoresist resin compositions do not sufficiently meet the characteristics required as the resin composition for a photoresist.
In the case of the resin compositions each having, as a photopolymerizable monomer, the foregoing vinyloxyalkylated product of novolac obtained by condensing a monohydric phenol and an aldehyde such as formalin disclosed in JP-A-60-7165, JP-A-63-71840, and JP-A-64-88538 described above, it is difficult to simultaneously obtain a high sensitivity and a developability with an aqueous diluted alkali solution, because of a small content of a phenolic hydroxy group in the monomer molecule.